Transmission device and transmission method

ABSTRACT

A GI insertion section  105  inserts a guard interval into transmission data. Delay addition sections  107 - 1, 107 - 2  set a delay time in the transmission data. An arrival time calculation section  115  calculates for each directivity an arrival time after data is transmitted from the other party of communication until the data is received from received data of each directivity. A delay time determining section  116  calculates a difference in the arrival time between transmission data transmitted with two directivities and sets the calculated arrival time difference in the transmission data to be transmitted with the directivity corresponding to the smaller arrival time as a delay time. A GI length determining section  117  sets a minimum arrival time of the calculated arrival times as a guard interval. This allows a transmission rate to be improved by shortening the length of a guard interval in a radio communication system to which a system of transmitting an OFDM signal with a directivity is applied.

TECHNICAL FIELD

The present invention relates to a transmission apparatus andtransmission method, and more particularly, to a transmission apparatusand transmission method for transmitting data according to an OFDMscheme with, for example, guard intervals inserted.

BACKGROUND Art

In a mobile communication system, an OFDM scheme is under study. OFDMuses a low symbol rate per carrier, and therefore using OFDM alone makesa system resistant to multipaths. Introducing guard intervals makes thesystem even more resistant to multipaths. Guard intervals can berealized by copying the waveform of a posterior portion of symbol datato the beginning of the symbol data. In this way, it is possible tocorrectly receive signals for a delay signals having a length shorterthan the guard interval length in an OFDM communication. However, sinceguard intervals do not have a role as data sections, the transmissionrate improves when guard intervals are as short as possible.

On the other hand, a system which sends an OFDM signal with directivityadded thereto is also under study. In the system which transmits datawith directivity, a base station transmits a signal with directivityoriented in the direction of arrival of an incoming signal from a mobilestation. When there is a plurality of directions of arrival, the basestation transmits data in the direction in which data is received withmaximum power from the mobile station or transmits data with a pluralityof directivities in the respective directions. The receiving side canobtain a path diversity effect from such signals transmitted with aplurality of directivities, and can thereby obtain data of good qualitywith fewer errors.

However, large delay time differences are produced among arrivingsignals transmitted with a plurality of directivities through theirrespective paths, and therefore the delay time differences may exceed arange of guard intervals unless sufficiently long guard intervals areinserted in transmission data compared to a case where signals aretransmitted with a single directivity. In order to prevent delay timedifferences from exceeding the guard interval range, there is a schemeunder which data is transmitted with a guard interval having the samelength as a maximum arrival time among arrival times for the respectivedirectivities after data is transmitted until the other party ofcommunication receives the data. According to this scheme, even whenlarge delay time differences are produced among incoming signals intheir respective paths, the delay time differences fall within the guardinterval range, and therefore no interference is produced among symbols.

However, in the case of a conventional transmission apparatus andtransmission method, when data is transmitted with a plurality ofdirectivities, a guard interval having the same length as that of themaximum arrival time among arrival times of the respective directivitiesis inserted, it is always necessary to design guard intervals accordingto the maximum arrival time, which leads to a problem that guardintervals are longer compared to a system in which signals aretransmitted with a single directivity.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a transmissionapparatus and transmission method in a radio communication system usinga system whereby an OFDM signal is transmitted with directivity, capableof improving the transmission rate by reducing the lengths of guardintervals.

This object can be attained by setting the lengths of guard intervalsand delay times for respective directivities when transmission data istransmitted based on information on arrival times of the respectivedirectivities after data is transmitted until the other party ofcommunication receives the data, inserting the guard intervals of theset lengths in transmission data and transmitting the transmission datawith a plurality of directivities according to the set delay times.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 2 is a schematic view illustrating a state in which a signal istransmitted with directivity from a base station apparatus to a mobilestation;

FIG. 3 illustrates a transmission timing when a guard interval is Tb;

FIG. 4 illustrates a reception timing when a guard interval is Tb;

FIG. 5 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 2 of the present invention; and

FIG. 6 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 2 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below.

Embodiment 1

FIG. 1 is a block diagram showing the configuration of a base stationapparatus 100 provided with a transmission apparatus according toEmbodiment 1.

A modulation section 101 modulates transmission data and outputs thetransmission data to an S/P conversion section 102.

The S/P conversion section 102 converts the transmission data input fromthe modulation section 101 from a serial data format to a parallel dataformat and outputs the parallel data to an IFFT section 103.

The IFFT section 103 applies inverse fast Fourier transform processingto the transmission data input from the S/P conversion section 102 andoutputs the processed data to a P/S conversion section 104.

The P/S conversion section 104 converts the transmission data input fromthe IFFT section 103 from a parallel data format to a serial data formatand outputs the serial data to a GI insertion section 105.

The GI insertion section 105 inserts a guard interval having a lengthdetermined by a GI length determining section 117 into the transmissiondata input from the P/S conversion section 104 and outputs thetransmission data to a data replication section 106.

The data replication section 106 replicates the transmission data inputfrom the GI insertion section 105 into two lines of data and outputs thedata to delay addition sections 107-1, 107-2. The transmission data isto be transmitted with directivities different between the two lines.

The delay addition sections 107-1, 107-2 set a delay time determined bya delay time determining section 116 in the transmission data input fromthe data replication section 106 and outputs the transmission data withdelay times to weight multiplication sections 108-1, 108-2.

The weight multiplication sections 108-1, 108-2, which are transmissionsections, assign weights to the transmission data input from the delayaddition sections 107-1, 107-2 based on information on a directivity ofa desired signal with maximum reception power input from a directivityreception section 114 and output the two lines of transmission data toas many adders 109-1 to 109-4 as antennas.

The adders 109-1 to 109-4 add up the two lines of transmission datainput from the weight multiplication sections 108-1, 108-2 and outputthe transmission data to transmission RF sections 110-1 to 110-4.

The transmission RF sections 110-1 to 110-4 apply processing such asup-conversion from a baseband frequency to a radio frequency to thetransmission data input from the adders 109-1 to 109-4, amplify theprocessed data and output to duplexers 111-1 to 111-4.

The duplexers 111-1 to 111-4 transmit the transmission data input fromthe transmission RF sections 110-1 to 110-4 with directivities fromantennas 112-1 to 112-4 and output signals received from the antennas112-1 to 112-4 to reception RF sections 113-1 to 113-4.

The reception RF sections 113-1 to 113-4 apply processing such asdown-conversion from a radio frequency to a baseband frequency to thereceived data input from the duplexers 111-1 to 111-4 and output theprocessed data to a directivity reception section 114.

The directivity reception section 114 forms two directivities using thereceived data input from the reception RF sections 113-1 to 113-4 andperforms reception processing using the directivities formed. Thedirectivity reception section 114 selects a directivity of a desiredsignal having maximum reception power from the result of signalsreceived with directivity and outputs the information on the selecteddirectivity to the weight multiplication sections 108-1, 108-2.Furthermore, after carrying out reception processing, the directivityreception section 114 outputs the received data to an arrival timecalculation section 115.

The arrival time calculation section 115, which is an arrival timeinformation acquisition section, calculates an arrival time after theother party of communication transmits a signal until the base stationapparatus 100 receives the signal from the received data input from thedirectivity reception section 114 and outputs the information on thecalculated arrival time to the GI length determining section 117 and thedelay time determining section 116.

The delay time determining section 116 determines a relative delay time(transmission delay time) of transmission data to be transmitted withrespective directivities based on the information on the arrival time ofthe two directivities input from the arrival time calculation section115. The delay time determining section 116 controls the delay additionsections 107-1, 107-2 so that the delay times determined for therespective directivities are set. A delay time is equal to a differencebetween arrival times of two directivities and set in transmission datato be transmitted with the directivity corresponding to the smallerarrival time.

The GI length determining section 117 selects the smaller arrival timeout of the arrival times of the two directivities based on theinformation on the arrival times input from the arrival time calculationsection 115 and outputs the information on the selected arrival time tothe GI insertion section 105.

Next, a scheme for setting a delay time for each directivity will beexplained using FIG. 2 to FIG. 5.

In FIG. 2, the base station apparatus 100 has the configuration shown inFIG. 1 and a mobile station 201 which is the other party ofcommunication is a conventional common mobile station. The same datatransmitted from the base station apparatus 100 with directivity A(first directivity) and directivity B (second directivity) are reflectedby reflecting objects 202, 203 such as buildings and arrive at themobile station 201. In this case, the transmission data transmitted withthe directivity A and transmission data transmitted with the directivityB from the base station apparatus 100 arrive at the mobile station 201at different arrival times Ta (first arrival time) and Tb (secondarrival time) (Ta>Tb). In this case, by delaying the transmission timingof the transmission data transmitted from the base station apparatus 100with a directivity B with respect to the transmission timing of thetransmission data transmitted with a directivity A by Ta−Tb, it ispossible to set the length of a guard interval of the transmission datatransmitted from the base station apparatus 100 to the arrival time Tbof the directivity B whose arrival time is smaller. That is, with regardto the received data received with the directivity A and directivity Bby the mobile station 201, even when the length of the guard interval isset to Tb, no interference occurs between symbols because the delay timeof the delay wave with respect to the advance wave is shorter than aguard interval. The reason will be explained below.

FIG. 3 and FIG. 4 show a transmission timing and a reception timing whenthe guard interval is set to Tb in the case of FIG. 2. FIG. 3 shows atransmission timing at the base station apparatus and FIG. 4 shows areception timing at the mobile station. In FIG. 3 and FIG. 4, thehorizontal axis shows time.

As shown in FIG. 3, the base station apparatus delays the transmissiontiming of transmission data 302 transmitted with the directivity B byTa−Tb with respect to the transmission timing of transmission data 301transmitted with the directivity A. That is, the transmission data 302with the directivity B is transmitted at time Tt₁ which is Ta−Tb behindtime Tt₀ at which the transmission data 301 with the directivity A istransmitted.

Then, as shown in FIG. 4, the transmission data 301 transmitted with thedirectivity A arrives at the mobile station at time Tr₂ after a lapse ofthe arrival time Ta from the time Tr₀. On the other hand, thetransmission data 302 transmitted with the directivity B arrives at themobile station after a lapse of the arrival time Tb from the time Tr₀,and therefore when the delay time Ta−Tb set by the base stationapparatus is added, the data arrives at the mobile station at the timeTr₂ after a lapse of the arrival time Ta from the time Tr₀.

After all, the transmission data 301 transmitted with the directivity Aand the transmission data 302 transmitted with the directivity B arriveat the same time Tr₂ and with regard to the guard interval of thedirectivity A and the guard interval of the directivity B, the delaytime difference between the two never exceeds the range of their guardintervals, and therefore no interference occurs between symbols evenwhen the length of the guard interval of the transmission data is set toTb.

Thus, according to the transmission apparatus and transmission method ofthis Embodiment 1, the GI insertion section inserts the smaller arrivaltime out of arrival times with respective directivities as a guardinterval and the delay addition section delays the transmission datatransmitted with a directivity with the smaller arrival time by thedifference between the arrival times with the respective directivities,and therefore the delay time difference of the received data neverexceeds the range of guard intervals and no interference between symbolsoccurs, and it is thereby possible to reduce the lengths of guardintervals and improve the transmission rate. Furthermore, thetransmission apparatus and transmission method of this Embodiment 1eliminates the necessity for a circuit which adjusts the delay timedifference so as to fall within the range of guard intervals and whichis conventionally required on the receiving side, and therefore it ispossible to make the circuit of the receiver as simple as possible anddownsize the receiver compared to the conventional example.

Embodiment 2

FIG. 5 illustrates the configuration of a base station apparatus 500provided with a transmission apparatus according to this Embodiment 2and FIG. 6 illustrates the configuration of a mobile station 600 whichis the other party of communication of the transmission apparatusaccording to this Embodiment 2.

The base station apparatus 500 according to Embodiment 2 of the presentinvention corresponds to the base station apparatus 100 according toEmbodiment 1 of the present invention shown in FIG. 1 with a modulationsection 501 and a modulation section 502 added and the arrival timecalculation section 115 replaced by a reception timing informationextraction section 503. The components having the same configuration asthat in FIG. 1 are assigned the same reference numerals and explanationsthereof will be omitted.

First, the configuration of the base station apparatus 500 will beexplained.

The modulation section 501 modulates a pilot signal 1 and outputs thepilot signal to weight multiplication sections 108-1, 108-2.

The modulation section 502 modulates a pilot signal 2 and outputs thepilot signal to weight multiplication sections 108-1, 108-2. The pilotsignal 1 and pilot signal 2 are pilot signals having different bitpatterns. Furthermore, any different pilot signals can be used when notonly the pilot signals have different bit patterns but also the pilotsignals can be distinguished from data.

The reception timing information extraction section 503, which is anarrival time information section, extracts reception timing information(information on an arrival time) of each directivity from received datainput from a directivity reception section 114 and outputs the receptiontiming information to a GI length determining section 117 and a delaytime determining section 116. The reception timing information isinformation on timings at which the pilot signal 1 and pilot signal 2are transmitted with different directivities simultaneously and timingsat which the other party of communication receives the pilot signal 1and pilot signal 2.

Next, the configuration of the mobile station 600 will be explainedusing FIG. 6.

An antenna 601 outputs received data with a plurality of directivitiesto a duplexer 602 and transmits transmission data output from theduplexer 602. The received data received by the antenna 601 includes thepilot signal 1 and pilot signal 2 transmitted from the base stationapparatus 500. Furthermore, the transmission data transmitted from theantenna 601 includes reception timing information which is informationon a difference between the reception timing of the pilot signal 1 andthe reception timing of the pilot signal 2.

The duplexer 602 separates received data from transmission data, outputsthe data received at the antenna 601 to a radio reception section 603and transmits transmission data input from a radio transmission section607 from the antenna 601.

The radio reception section 603 down-converts the received data inputfrom the duplexer 602 from a radiofrequency to a baseband frequency andoutputs the received data to a demodulation section 604.

The demodulation section 604 demodulates the received data input fromthe radio reception section 603, obtains the received data and outputsthe demodulation result to a reception timing detection section 605.

The reception timing detection section 605 detects reception timingscorresponding to the directivity of the pilot signal 1 and directivityof the pilot signal 2 from the received data input from the radioreception section 603 and outputs reception timing information on therespective detected directivities to a modulation section 606.

The modulation section 606 modulates transmission data including thereception timing information input from the reception timing detectionsection 605 and outputs the modulated transmission data to the radiotransmission section 607.

The radio transmission section 607 up-converts the transmission datainput from the modulation section 606 from a baseband frequency to aradio frequency and outputs the transmission data to the duplexer 602.

Next, the operations of the base station apparatus 500 and mobilestation 600 will be explained using FIG. 2, FIG. 5 and FIG. 6.

The pilot signal 1 and pilot signal 2 are modulated by the modulationsections 501, 502, weighted by weight multiplication sections 108-1,108-2 and then transmitted with different directivities simultaneously.At this time, the base station apparatus 500 transmits the pilot signal1 with directivity A and transmits the pilot signal 2 with directivityB.

Next, in the mobile station 600 which has received the pilot signal 1and pilot signal 2, the reception timing detection section 605 detectsreception timings of the directivity A and directivity B and transmitsthe transmission data with the detected reception timing informationincluded therein to the base station apparatus 500. In the base stationapparatus 500 which has received the received data including thereception timing information, the reception timing informationextraction section 503 extracts the reception timing information fromthe received data, the GI length determining section 117 selects amaximum delay time of the minimum directivity B among maximum delaytimes of the respective directivities as a GI length and a GI insertionsection 105 inserts a guard interval having the same time as the delaytime of the directivity B into the transmission data to be transmittedwith the directivity A and directivity B. Furthermore, delay additionsections 107-1, 107-2 set a delay time of Ta−Tb from transmission timeTt₀ of the transmission data with the directivity A for the transmissiondata with the directivity B from the reception timing information andtransmits the transmission data with the directivity A and directivityB. The method of setting a guard interval and the method of setting adelay time for the transmission data are the same as those in Embodiment1, and therefore detailed explanations thereof will be omitted.

Thus, in addition to the effect of Embodiment 1 above, the transmissionapparatus and transmission method according to this Embodiment 2 canadjust a directivity with which pilot signals are transmitted and adirectivity with which data is transmitted so as to precisely coincidewith each other, and can thereby insert a guard interval with fewererrors and with high precision by determining the length of the guardinterval based on the information on an arrival time detected usingpilot signals. Furthermore, the transmission apparatus and transmissionmethod according to this Embodiment 2 allows the arrival time of eachdirectivity to be known based on a reception timing at a mobile stationof a pilot signal transmitted from a base station apparatus, andtherefore this embodiment is also applicable to a base station apparatuswhich communicates with a mobile station to which data is nottransmitted with directivity.

Embodiment 1 and Embodiment 2 assume that the same transmission data aretransmitted with two directivities; directivity A and directivity B, butthe present invention is not limited to this and it is also possible totransmit the same transmission data with three or more directivities. Inthis case, even when the guard interval to be inserted into transmissiondata to be transmitted with all directivities is set to the same arrivaltime corresponding to a directivity of a minimum arrival time, nointerference between symbols occurs.

Furthermore, Embodiment 1 and Embodiment 2 assume that the sametransmission data is transmitted with different directivities, but thepresent invention is not limited to this and it is also possible totransmit different transmission data with different directivitiesFurthermore, Embodiment 1 and Embodiment 2 have described the case wherethe mobile station does not transmit data with directivity, but thepresent invention is not limited to this and it is also possible for themobile station to transmit data with directivity.

Embodiment 1 and Embodiment 2 assume that transmission data is weightedat the weight multiplication section and transmitted with directivity,but the present invention is not limited to this and transmission datacan also be transmitted with directivity without any weight assigned.

As explained so far, according to the present invention, a radiocommunication system to which a system of transmitting an OFDM signalwith directivity is applied can improve its transmission rate byshortening the length of a guard interval.

This application is based on the Japanese Patent Application No.2003-29340 filed on Feb. 6, 2003, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention relates to a transmission apparatus andtransmission method and is suitable for use in, for example, atransmission apparatus and transmission method for transmitting datawith a guard interval inserted under an OFDM scheme.

[FIG. 1]

-   TRANSMISSION DATA-   101 MODULATION SECTION-   102 S/P CONVERSION SECTION-   103 IFFT SECTION-   104 P/S CONVERSION SECTION-   105 GI INSERTION SECTION-   106 DATA REPLICATION SECTION-   107-1 DELAY ADDITION SECTION-   116 DELAY TIME DETERMINING SECTION-   117 GI LENGTH DETERMINING SECTION-   115 ARRIVAL TIME CALCULATION SECTION-   108-1 WEIGHT MULTIPLICATION SECTION-   114 DIRECTIVITY RECEPTION SECTION-   110-1 TRANSMISSION RF SECTION-   110-2 TRANSMISSION RF SECTION-   110-3 TRANSMISSION RF SECTION-   110-4 TRANSMISSION RF SECTION-   113-1 RECEPTION RF SECTION-   113-2 RECEPTION RF SECTION-   113-3 RECEPTION RF SECTION-   113-4 RECEPTION RF SECTION-   111-1 DUPLEXER-   111-2 DUPLEXER-   111-3 DUPLEXER-   111-4 DUPLEXER    [FIG. 2]-   202 REFLECTING OBJECT-   DIRECTIVITY A-   100 BASE STATION APPARATUS-   DIRECTIVITY B-   203 REFLECTING OBJECT-   201 MOBILE STATION    [FIG. 3]-   DIRECTIVITY A-   301 DATA-   DIRECTIVITY B-   302 DATA-   TIME    [FIG. 4]-   DIRECTIVITY A-   301 DATA-   DIRECTIVITY B-   302 DATA-   TIME    [FIG. 5]-   TRANSMISSION DATA-   101 MODULATION SECTION-   102 S/P CONVERSION SECTION-   103 IFFT SECTION-   104 P/S CONVERSION SECTION-   105 GI INSERTION SECTION-   106 DATA REPLICATION SECTION-   107-1 DELAY ADDITION SECTION-   PILOT SIGNAL 1-   PILOT SIGNAL 2-   501 MODULATION SECTION-   502 MODULATION SECTION-   117 GI LENGTH DETERMINING SECTION-   116 DELAY TIME DETERMINING SECTION-   503 RECEPTION TIMING INFORMATION EXTRACTION SECTION-   108-1 WEIGHT MULTIPLICATION SECTION-   114 DIRECTIVITY RECEPTION SECTION-   110-1 TRANSMISSION RF SECTION-   110-2 TRANSMISSION RF SECTION-   110-3 TRANSMISSION RF SECTION-   110-4 TRANSMISSION RF SECTION-   113-1 RECEPTION RF SECTION-   113-2 RECEPTION RF SECTION-   113-3 RECEPTION RF SECTION-   113-4 RECEPTION RF SECTION-   111-1 DUPLEXER-   111-2 DUPLEXER-   111-3 DUPLEXER-   111-4 DUPLEXER    [FIG. 6]-   602 DUPLEXER-   608 RADIO RECEPTION SECTION-   607 RADIO TRANSMISSION SECTION-   604 DEMODULATION SECTION-   RECEIVED DATA-   605 RECEPTION TIMING DETECTION SECTION-   606 MODULATION SECTION-   TRANSMISSION DATA

1. A transmission apparatus comprising: an arrival time informationacquisition section that acquires information on an arrival time of eachdirectivity after transmission data is transmitted until the other partyof communication receives the transmission data; a guard intervalinsertion section that inserts a guard interval having a lengthdetermined based on said arrival time information into transmissiondata; a transmission delay section that sets a transmission delay timein transmission data for each said directivity based on said arrivaltime information; and a transmission section that transmits the sametransmission data with a plurality of said directivities.
 2. Thetransmission apparatus according to claim 1, wherein said arrival timeinformation acquisition section acquires information on a first arrivaltime of transmission data to be transmitted with a first directivity andinformation on a second arrival time, which is smaller than said firstarrival time, of transmission data to be transmitted with a seconddirectivity, said guard interval insertion section inserts the samelength of guard interval as said second arrival time, and saidtransmission delay section delays the transmission timing of thetransmission data to be transmitted with said second directivity by adifference between said first arrival time and said second arrival timewith respect to the transmission timing of the transmission data to betransmitted with said first directivity.
 3. The transmission apparatusaccording to claim 1, wherein said transmission section transmits apilot signal which differs from one said directivity to another, andsaid arrival time information acquisition section acquires informationon said arrival time by extracting information on the time after a pilotsignal is transmitted until the other party of communication receivessaid pilot signal from the received signal.
 4. A base station apparatusprovided with a transmission apparatus, said transmission apparatuscomprising: an arrival time information acquisition section thatacquires information on an arrival time of each directivity aftertransmission data is transmitted until the other party of communicationreceives the transmission data; a guard interval insertion section thatinserts a guard interval having a length determined based on saidarrival time information into transmission data; a transmission delaysection that sets a transmission delay time in transmission data foreach said directivity based on said arrival time information; and atransmission section that transmits the same transmission data with aplurality of said directivities.
 5. A communication terminal apparatusprovided with a transmission apparatus, said transmission apparatuscomprising: an arrival time information acquisition section thatacquires information on an arrival time of each directivity aftertransmission data is transmitted until the other party of communicationreceives the transmission data; a guard interval insertion section thatinserts a guard interval having a length determined based on saidarrival time information into transmission data; a transmission delaysection that sets a transmission delay time in transmission data foreach said directivity based on said arrival time information; and atransmission section that transmits the same transmission data with aplurality of said directivities.
 6. A transmission method comprising: astep of acquiring a first arrival time after transmission data istransmitted with a first directivity until the other party ofcommunication receives the transmission data; a step of acquiringinformation on a second arrival time, which is smaller than said firstarrival time after transmission data is transmitted with a seconddirectivity until the other party of communication receives thetransmission data; a step of inserting the same length of guard intervalas said second arrival time into the transmission data; a step ofdelaying the transmission timing of the transmission data to betransmitted with said second directivity by a difference between saidfirst arrival time and said second arrival time with respect to thetransmission timing of the transmission data to be transmitted with saidfirst directivity; and a step of transmitting the same transmission datawith a plurality of said directivities.